A hand-held electric tool with a main shaft that oscillates reciprocally around an axle center thereof to drive tool accessories for various operations has been extensively applied in a variety of fields. Such hand-held electric tool includes a housing, a motor, an oscillator device and a main shaft. Usually, the oscillator device of the electric tool has an axle center and a crank component (eccentric shaft) that is parallel to an axle center of a crank arm. A spherical bearing on the crank arm is connected with a connecting rod component (oscillating bar) through a sliding pair. Sliding friction between the crank component and the connecting rod component of the hand-held electric tool generates lots of heat to result in low mechanical efficiency. A cutter is easily heated when the hand-held electric tool cuts, especially cuts a metal material for a long time. Moreover, high temperature is transferred to the main shaft and the housing to lead to improper operation, even danger. Due to failure of a dust-proof component, the hand-held electric tool easily causes reduction of the efficiency of a bearing supporting the main shaft, even failure. Many technology improvement schemes for the electric tool are provided in this industry, but there are still some shortcomings.